Psychotic experiences such as hearing voices have classically been viewed as representative of severe forms of mental illness. However, recent research has begun to suggest that low level psychotic phenomena may be more common than previously thought (van Os et al. 2008). These experiences are mainly transitory, resolving in between 75-90% of cases.

Psychotic symptoms are also common in mental disorders previously classified as non-psychotic, for example mood disorders (Kelleher et al. 2011).

The development of these symptoms is known to be associated with exposure to trauma; for example childhood bullying or abuse (Kelleher et al. 2013). The presence of dose-response relationships and cessation of psychotic phenomena on removal of trauma suggests a causative relationship.

What is unclear is the mechanism linking childhood experience and psychotic phenomena; not all children exposed to abuse will go onto develop psychotic symptoms for example.

To increase understanding in this area, recent research published in the British Journal of Psychiatry seeks to explore further the interplay of risk factors; adverse life events, childhood adversity and cannabis use with the development of low-level psychotic experiences (Morgan et al. 2014).

This study explores the impact of childhood adversity and negative life events on the experience of psychotic phenomena

Methods

The authors made use of a cross-sectional study design to address their hypotheses:

Childhood adversity, life events and cannabis would be associated singly and cumulatively with psychotic experiences

Childhood abuse would combine synergistically with

Life events

Cannabis use

Participant interviews

Participants were recruited from households within the target area (South East London) and involved all household residents aged 16 or older

Computer-assisted face to face interviews were used to collect data

The psychosis screening questionnaire (a standardised measure) was used to screen for psychotic experiences. It assessed:

Thought disorder

Paranoia

Strange experiences

Hallucinations

Questions were asked relating to childhood experiences of physical and sexual abuse

Sociodemographic and socioeconomic information were gathered

Previous illicit substance and cannabis use was recorded

Symptoms of common mental disorder were recorded, using a structured clinical interview schedule

Data analysis

Participants who reported a past diagnosis of psychotic disorder were excluded from the analysis.

To assess their hypotheses, the authors initially used a logistic regression approach to explore the relationship between childhood adversity, life events and cannabis use with psychotic experiences. Remaining data were used as possible confounding variables.

They also tested for an additive synergistic interaction between childhood abuse and life events or cannabis use; that is, do those exposed to both childhood abuse and cannabis use experience a greater risk of psychotic events than the sum of risks for those exposed to childhood abuse and cannabis use alone?

Results: the risk of psychotic experiences

In total, after exclusion for missing data and previous psychotic disorder diagnosis, the authors had access to data for 1,680 participants (mean age 39, 44% men)

17.9% of participants described psychotic experiences in the past year

Paranoia was the most commonly endorsed experience (13.2%)

Factors associated with increased psychotic experiences included:

Young age (16-29 years vs 30+ years)

Ethnicity (Other than White British)

Unemployment

Any common mental disorder (mixed anxiety/depression, depression or anxiety)

University level education was associated with a decrease in risk for psychotic experience

Cannabis use in the past year, but not prior, was associated with an increased risk for psychotic experience

Nearly 1 in 5 participants described psychotic experiences and adverse life events were nearly universal

Each event experienced in the past year added an additional OR 1.7 (95% CI 1.44 to 2.00)

Synergistic interactions

There was statistically significant evidence of an additive synergistic interaction between childhood abuse and experienced life events

Cannabis use in the past year and past childhood abuse interacted with a suggestion of synergism, but this was not statistically significant

There was evidence of a synergistic interaction between childhood abuse and negative life events

Conclusions

The authors conclude:

Our findings are consistent with the hypothesis that childhood abuse creates an enduring vulnerability to psychosis that is realised in the event of exposure to further stressors and risk factors.

Discussion

This paper adds additional evidence for the interaction between childhood abuse, adverse life events and psychotic experience. Being a cross-sectional design it cannot demonstrate causation and further study, as always, is required to explore the nature of these observations in further detail.

The study is also limited by its superficiality – for example the nature of the alleged psychotic phenomena has not been explored in detail and in relation to endorsed life events; the most commonly endorsed experience (paranoia) could be seen as appropriate after one has been injured with a weapon for instance? Similarly the amount of cannabis use and impact of psychotic phenomena on personal life remains unexplored here.

Despite these limitations this study serves as further support of the need for detailed consideration of life events during clinical assessment, as their presence, and likely the individual’s interpretation of this experience, are related to the experience of psychotic phenomena.

Enquiring about childhood experiences and negative life events is a crucial part of all clinical assessments

Following completing his PhD Andrew has recently returned to full time clinical practice and is currently trying to acclimatise to life back within the NHS... He maintains his research interests and will take up a clinical lectureship post from February.